1. Field of the Disclosure
The present disclosure relates to an organic light-emitting diode (OLED) display device, and particularly, to an OLED display panel capable of minimizing degradation due to inflow of moisture thereinto, using a flexible characteristic by a plastic substrate, the degradation resulting from a large stair gap between a bank and an interlayer insulating layer.
2. Background of the Disclosure
Flat panel display devices, which have been proposed to replace the conventional cathode ray tube (CRT) display devices, may be categorized into liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP) and organic light-emitting diode (OLED) displays, etc.
Among the flat panel display devices, the OLED display device has a characteristic that an organic light-emitting diode (EL) provided on a display panel has high brightness and a low operation voltage. Further, the OLED display device has a high contrast ratio because it is a spontaneous light-emitting type, and it can implement a display of an ultra thin thickness. The OLED display device can easily implement moving images due to a short response time corresponding to several micro seconds (μs). Besides, the OLED display device has no limitation in a viewing angle, and has a stable driving characteristic even at a low temperature.
FIG. 1 is a view illustrating an equivalent circuit with respect to one pixel of an organic light-emitting diode (OLED) display panel in accordance with the conventional art.
As shown, the OLED display panel comprises a scan line (SL), a data line (DL) crossing the scan line (SL), and a power supply line (VDDL) spaced from the scan line (SL) and the data line (DL). By the scan line (SL), the data line (DL) and the power supply line (VDDL), a single pixel (PX) is defined.
The OLED display panel further comprises a switching transistor (SWT) for applying a data signal (Vdata) to a first node (N1) in correspondence to a scan signal (Scan); a driving transistor (DT) for receiving a driving voltage (VDD) by a source electrode, and applying a drain current to an organic light-emitting diode (EL) according to a voltage difference between a gate electrode and a source electrode, the voltage difference determined by a voltage applied to the first node (N1); and a capacitor (C1) for maintaining a voltage applied to the gate electrode of the driving transistor (DT) for a single frame.
The organic light-emitting diode (EL) comprises an anode connected to a drain electrode of the driving transistor (DT), a cathode which is grounded (VSS), and an organic light-emitting layer formed between the anode and the cathode. The organic light-emitting layer may be composed of a hole transporting layer, an emitting material layer, and an electron transporting layer.
FIG. 2A is a view schematically illustrating a structure of an OLED display panel in accordance with the conventional art, and FIG. 2B is a sectional view taken along line ‘II-II’ in FIG. 2A.
Referring to FIGS. 2A and 2B, the conventional OLED display panel has a active area (NA) formed on a substrate 10, and a non-active area (N/A) formed outside the active area (A/A). A plurality of pixel regions (PX) defined by scan lines (SL) and data lines (DL) are provided in the display active area (NA), and power supply lines (VDDL) are provided in parallel to the data lines (DL). Especially, the non-active area (N/A) of the OLED display panel has a multi-layered structure extending from the active area (A/A). A gate insulating layer 15, an insulating layer 19, an interlayer insulating layer 25, a bank 33, a first passivation layer 39, an adhesive layer 41, and a barrier film 50 are sequentially formed on a substrate 11, in at least the non-active area (N/A).
Such structure is called ‘face seal’ structure. In the lamination structure of the passivation layer 39, the adhesive layer 41 and the barrier film 50, the passivation layer 39 and the barrier film 50 serve as a barrier which prevents moisture permeability into the OLED display panel. However, the adhesive layer 41 does not serve well as a barrier, resulting in introduction of water from the side surface of the OLED display panel.
In the face seal structure, the side surface of the OLED display panel, formed by the interlayer insulating layer 25 and the bank 33, has a wide inclination angle. Due to such wide inclination angle, the foreign materials (DP) remain at the side surface of the OLED display panel without being removed, during fabrication processes. This may cause water to be introduced into the OLED display panel from outside.
Water (W), which has been introduced through the adhesive layer 41 having a low barrier function, is firstly introduced into the OLED display panel through a contact part between foreign materials and the OLED display panel. Then, the water is secondarily introduced into the OLED display panel through a bank, a planarization layer, etc. This may cause the cathode of the organic light-emitting diode (EL), thereby degrading reliability of the OLED display panel.